Parasitic Diseases of Zoonotic Importance in Humans of Northeast India, with Special Reference to Ocular Involvement
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Eye and Brain Dovepress open access to scientific and medical research Open Access Full Text Article REVIEW Parasitic diseases of zoonotic importance in humans of northeast India, with special reference to ocular involvement Dipankar Das1 Abstract: Parasitic zoonotic diseases are prevalent in India, including the northeastern states. Saidul Islam2 Proper epidemiological data are lacking from this part of the country on zoonotic parasitic Harsha Bhattacharjee1 diseases, and newer diseases are emerging in the current scenario. Systemic manifestation Angshuman Deka1 of such diseases as cysticercosis, paragonimiasis, hydatidosis, and toxoplasmosis are fairly Dinakumar Yambem1 common. The incidence of acquired toxoplasmal infection is showing an increasing trend Prerana Sushil Tahiliani1 in association with acquired immunodeficiency syndrome. Among the ocular parasitic dis- eases, toxoplasmosis, cysticercosis, toxocariasis, dirofilariasis, gnathostomiasis, hydatidosis, Panna Deka1 amebiasis, giardiasis, etc, are the real problems that are seen in this subset of the population. Pankaj Bhattacharyya1 Therefore, proper coordination between various medical specialities, including veterinary 1 Satyen Deka science and other governing bodies, is needed for better and more effective strategic planning 1 Kalyan Das to control zoonoses. 1 Gayatri Bharali Keywords: zoonoses, regional infections, toxoplasmosis, cysticercosis, toxocariasis, 1 Apurba Deka hydatidosis Rajashree Paul1 1Sri Sankaradeva Nethralaya, Introduction Guwahati, 2Department of Parasitology, College of Veterinary India is the second-most densely inhabited and seventh-largest country in the world, Science, Assam Agricultural University, and there is a lot of variation in the geographic areas, ethnicity, religion, food habits, Guwahati, Assam, India personal behavior, level of education, and standard of living.1 The recent census of the country showed that 72.2% of the population lived in rural areas, with over 70% of this population owning livestock, which play an important role in the causation of zoonotic diseases in humans. Parasitic zoonoses affect human as well as animal health directly and indirectly, which may affect the socioeconomic condition of the country as a whole. Poor economic conditions, sanitation, water supply, and personal habits are some of the causes on the Indian subcontinent of harboring the zoonoses, particularly in the northeast part of India.1 This paper focuses on important parasitic zoonoses in Assam and other northeastern states of India. Toxoplasmosis 2 Correspondence: Dipankar Das Toxoplasmosis is a common disease in both mammals and birds. The disease is caused Department of Ocular Pathology, by the obligate intracellular protozoan Toxoplasma gondii. Intermediate hosts include Uveitis and Neuro-Ophthalmology Services, Sri Sankaradeva Nethralaya, sheep, goats, pigs, and humans. Oocysts of T. gondii are uniquely found in the intestinal Beltola, Guwahati, Assam 781028, India mucosa of cats (definitive hosts). Once they are released, they spread to humans and Tel +91 361 222 8879/230 5516 other animals through a variety of vectors. Toxoplasmosis in the central nervous system Fax +91 361 222 8878 Email [email protected] is nowadays seen in acquired immunodeficiency syndrome (AIDS) patients in India.3 submit your manuscript | www.dovepress.com Eye and Brain 2014:6 1–8 1 Dovepress © 2014 Das et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License. The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further http://dx.doi.org/10.2147/EB.S64404 permission from Dove Medical Press Limited, provided the work is properly attributed. Permissions beyond the scope of the License are administered by Dove Medical Press Limited. Information on how to request permission may be found at: http://www.dovepress.com/permissions.php Das et al Dovepress Serum IgA titers in enzyme-linked immunosorbent assays sign of acquired active toxoplasmosis is a whitish yellow (ELISAs) are positive in chronic toxoplasmosis, whereas IgM retinal lesion associated with hazy vitreous as a result of the is positive in acute infection. Therefore, the titers for both presence of vitreous cells (“headlight in the fog” appearance). IgG and IgM are important, and need to be strongly corre- Old retinochoroidal scars can often be seen adjacent to the lated with clinical findings. In a national serological survey new whitish yellow lesion. The areas of retinitis are the in India,4 a total of 23,094 serum samples were tested for result of tissue-cyst bursting and releasing bradyzoites that antibodies to the parasite. IgG and IgM antibodies were found transform into tachyzoites, which in turn invade the neigh- to be positive in 24.3% and 2% of the samples, respectively. boring cells. These destructive lesions are usually larger The lowest seroprevalence value was obtained in north India, than one disk diameter, and appear as soft, white, fluffy while it was highest in the south.4 The data probably indicate infiltrates surrounded by retinal edema with choroiditis.9–11 the effect of significantly drier conditions in the north, leading When the tachyzoites come under increasing attack by the to reduced survivability of T. gondii oocysts. host’s immune response, they gradually transform back into Our previous study,5 conducted in a tertiary eye-care cen- inflammatory exudates, and are frequently present around the ter in one of the northeast states (Assam) of India, showed 37 retinal vessels adjacent to an area of active inflammation. cases of toxoplasmal uveitis (40.21%) in 1 year compared to Chorioretinal scars are occasionally found in uninvolved 27.87% by Biswas et al6 from south India. Out of the 37 cases, areas. Patients often complain of blurred vision, floaters, 14 were acquired, while 23 cases were congenital toxoplasmal photophobia, and pain in the affected eye. Occasionally, retinochoroidal lesions. Serum IgG only was positive in 30 of the initial presentation would be severe unilateral papillitis, 37 cases and IgM only in three cases, while both serum IgG macular hard exudates distributed in star-like fashion, and and IgM positivity was observed in four cases. Chorioretinitis vitreal inflammation simulating neuroretinitis. Multifocal was the most common presentation, seen in about 95.6% of active toxoplasmosis simultaneously involving both the cases. T. gondii tends to affect the macula due to the high retina and the optic nerve is unusual, but was documented oxygen content owing to the end-arterial system of the retinal in an immunocompromised patient with human immuno- circulation. Retinochoroiditis is a more appropriate term for deficiency virus (HIV) infection. Differential diagnosis of acute inflammation, as the organism first lodges in the retina toxoplasmal lesions could be tuberculous granuloma, fungal followed by the choroid. endophthalmitis, sarcoid, syphilitic retinitis, cytomegalovirus The prevalence of toxoplasmosis in India shows a wide infection, intraocular lymphoma, and toxocariasis. variation. One study showed as high as 77% in women in the Histopathologically, the toxoplasmal lesion shows reproductive age-group.7 There is a report of this parasitic necrosis of the involved retina, with destruction of retinal infection among pregnant women in northeast India. In a architecture and underlying choroid. Since the parasite has study done by Borkakoty et al, the seroprevalence of T. gon- a propensity for attacking the neural tissue, the trophozoites dii infection was observed to be 44.6% and 36.8% among and the cysts are usually found in the superficial layers pregnant women with and without history of pregnancy of the retina within the areas of necrosis. The infiltrate wastage, respectively.8 A higher prevalence of T. gondii consists predominantly of lymphocytes, macrophages, and infection has been observed in women belonging to the epithelioid cells, with plasma cells found in the periphery lower socioeconomic class.8 It has also been observed that of the lesion.9,11,12 Cell-mediated immunity is said to be the the seroprevalence of T. gondii in humans in India is lower major defense mechanism against toxoplasmal infection. compared to their Western counterparts. This may be due to In patients with ocular toxoplasmosis, the cellular immune a preference for dogs as pets rather than cats in the Western responses appear to be directed predominantly against sur- population. face protein P22. However, some evidence also indicates The majority of reported cases of ocular toxoplasmosis that part of the disease may be mediated by autoimmune are congenital. The clinical manifestations of congenital mechanism directed against certain retinal antigens.12 ocular toxoplasmosis in infants include microphthalmia, The role of humoral response in toxoplasmosis remains enophthalmos, ptosis, nystagmus, choroidal coloboma, unclear. and strabismus.9,10 Posterior uveitis is the most common Ocular toxoplasmosis can be frequently diagnosed clini- manifestation, and presents as necrotizing retinitis usually cally on the basis of its characteristic retinochoroidal scar and adjacent to a larger atrophic retinochoroidal scar, which is inflammation. Serological testing confirms the clinical diag- often located in the macula in congenital cases. The critical nosis. There may be a history of eating undercooked